The temperature increase is normal. In 2D mode a card general runs at lower clockspeeds, voltages and fanspeeds. Further big parts of the gpu are unused, so when you move to 3D the GPU will become a lot hotter.

The cause of squeky noise coming from your loudspeakers is likely related to your powersupply. A videocard consumes a lot of power (~100W) and drains the PSU a lot. The 'quality' of the current it creates can decrease in case of a cheap PSU (the current becomes less stable). Soundcards can be sensitive to this.

Comparing to windows, this is not normal though. I tried the same glui example code under windows and didn't have 1C / 1 second increment. This makes me think there are some issues with the driver. That was the reason I mentioned this here. (neither my PSU is a cheap one)

Whatever game I played max temp I've seen was 55C (with no high freq. noise) in my system.

Of course when you do that the running rate of a program like glxgears is very much limited (for example from 5000 to 60 fps) so it is not surprising that the power use of the GPU decreases a lot by that.
I would be happy with 55C. My 6600GT GPU is consistently at over 70C even in 2D mode.